Blower designed for fitting particularly in a chamber furnace

ABSTRACT

The blower designed particularly for fitting in a chamber furnace has the hub of the rotor wheel in the shape of a solid of revolution with its slant height described by n degree polynomial and its Dp 2  outlet diameter greater than Dp 1  inlet diameter and the outward diameter of the axial and radial rotor wheel with spatially shaped blades monotonically increasing towards the flow from D 1   z  inlet diameter to D 2   z  outlet diameter.

This invention relates to a blower designed for fitting in a chamberfurnace in particular and used, among others, in furnaces for annealingof aluminium sheet.

In furnaces requiring circulation of hot gases, usually radial or axialblowers are used. The fitting of the latter is subject to significantrestrictions that affect their operating parameters. Due to theconditions of the bearings operation, the blowers are usually built asoverhung. In order to avoid excessive overhang and unnecessary increaseof the furnace chamber size, rotor wheels are fitted close to thechamber wall. This is also the reason for insufficient space for thestationary airfoils, which, in turn, considerably affects the efficiencyand flow parameters of the axial blower. Therefore, the parameters ofsuch blowers do not usually exceed the value of pressure difference Ψequalling 0.2 and the value of flow ψ equalling 0.3.

As compared to axial blowers, radial blowers used in furnaces ensureconsiderably greater pressure increments (with Ψ pressure differenceexceeding 0.4) however they are burdened with significant defects. Firstof all, in order to achieve the required pressure increment, the dynamicpressure should be recovered in a reasonably efficient manner. Inclassic designs of blowers this is done in cumulative spirals with largeangles of wrap, i.e. up to 360°. In chamber furnaces, air exhausted fromthe blower must go in two opposite ways. The use of one or two exhaustspirals is very difficult for structural reasons. In practice thisresults in an unequal distribution of velocities on both exhaustsurfaces of the blower, which is even magnified by existence of aconsiderable angular momentum of the agent behind the rotor wheel. Suchdefects are typical of radial and drum blowers.

The description of the patent No. DE 10022788 presents a solutioninvolving a use of an axial rotor with a constant outward diametercooperating with two flat diffusers turning into two nozzle boxes. Thisblower is characterised by the same flow parameters as typical axialblowers, however, it shows much greater pressure increments and ensuresan equal flow of the agent in both ways. Additionally, such blowers donot require using additional stators for the purposes of levelling ofthe field of velocity. However, the circulation efficiency of suchblowers is relatively low (0.4). One of the reasons for such a lowcirculation efficiency is the fact that the agent leaving the axialrotor has a great kinetic energy and, therefore, losses generated in thebridge at the angle of 90° are also considerable, as diffusers operatewith a rotational stall at the outlet.

The invented blower, particularly the one to be fitted in a chamberfurnace, in the form of a rotor wheel with blades set diagonally on theshaft, set in an enclosure creating an inlet confuser duct, with itsbridge with an approximate angle of 90° behind the rotor wheel, whichturns smoothly into a radial diffuser, behind which it has a bridgeshaped with an approximate angle of 90° ending with a nozzle box withnozzles is characterised in that the hub of the rotor wheel has theshape of a solid of revolution with its slant height described by ndegree polynomial and its Dp₂ outlet diameter greater than Dp₁ inletdiameter and the outward diameter of the axial and radial rotor wheelwith spatially shaped blades monotonically increasing towards the flowfrom D1 z inlet diameter to D2 z outlet diameter.

The presented solution, owing to the shape of the rotor allowing theshaping of the first bridge with a large angle, will enable an increasein the circulation efficiency and, at the same time, maintain therequired thermodynamic parameters.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be shown on an exemplary drawing, which does notrestrict its construction as shown in the drawing, in which FIG. 1presents a cross-section of the blower on the plane passing through itslongitudinal axis and bridge axis, whereas

FIG. 2 presents a cross-section of the hub and the blade of the rotorwheel.

On the blower shaft 1 there is a diagonally set rotor wheel 3 withspatially shaped blades 4. The wheel 3 is set in the enclosure 5,creating the inlet confuser duct 6. Behind the rotor wheel 3 the blowerhas a bridge 7 with an approximate angle of 90°, which turns smoothlyinto a radial diffuser 8, behind which there is another bridge 9 with anapproximate angle of 90°, ending with a nozzle box 10 with nozzles 11.The hub 12 of the rotor wheel 3 has the shape of a solid of revolutionwith its slant height described by n degree polynomial, with its Dp₂outlet diameter greater than Dp₁ inlet diameter and the outward diameterof the axial and radial rotor wheel 3 with spatially shaped blades 4,monotonically increasing towards the flow from D1 z inlet diameter to D2z outlet diameter. The rotor wheel 3 is a semi-open wheel without acover. Between the external contours of the blades 4 and the stationarybody of the blower there is gap δ, the size of which depends on mutualthermal dilatation of the wheel 3 and the body. It is also possible todeliver a blower, in which the wheel structure 3 is equipped with acover.

The hot air or other gas flows through the stationary duct 6, gainingacceleration of several percent, which favours levelling of the velocityprofile on the inlet surface of the rotor wheel 3. The direction of theflow of the agent onto the blades 4 of the rotor wheel 3 isapproximately axial. Next, the agent flows through the system of blades4 of the rotor wheel 3, which conveys energy to the agent in accordancewith the basic equation for fluid flow machines (Euler's identity). Theagent is subject to compression. The degree of compression depends upona selection of geometrical parameters of the rotor wheel 3 and itsrotating velocity. The agent leaves the rotor wheel 3 at an angle inrelation to the rotor rotation axis 3—diagonally. The γ flow-out angleon the meridional plane is described by γ relation <90°. The flow-outangle for the agent leaving the rotor wheel 3 depends on the assumedangle of the blade at the outlet and assumed rotating velocity.

1. The blower designed particularly for fitting in a chamber furnace, inthe form of a rotor wheel with blades set diagonally on the shaft, setin an enclosure creating an inlet confuser duct, with its bridge with anapproximate angle of 90° behind the rotor wheel, which turns smoothlyinto a radial diffuser, behind which it has a bridge shaped with anapproximate angle of 90° ending with a nozzle box with nozzles whereinthe hub of the rotor wheel has the shape of a solid of revolution withits slant height described by n degree polynomial and its Dp₂ outletdiameter greater than Dp₁ inlet diameter and the outward diameter of theaxial and radial rotor wheel with spatially shaped blades monotonicallyincreasing towards the flow from D1 z inlet diameter to D2 z outletdiameter.